Dynamic balance measurement station for a disc drive

ABSTRACT

An apparatus of automatically measuring the dynamic imbalance of a disc stack of a disc drive assembly, the disc stack conveyed to a first selected position in a balance measure assembly station where a rotary positioner lifts and rotates the disc stack above a sensor to locate an electrical lead of the disc drive motor. The disc stack is positioned in a reference position to position the electrical leads a for powering the disc drive motor. The disc stack is then conveyed to a second selected position where a motor power assembly clamps and powers the motor and discs. A balance head assembly measures the magnitude and phase angle of the dynamic imbalance of the disc stack and records the measurement to a production control computer.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/062,163 entitled AUTOMATED DISC PACK BALANCE MEASURE TOOL, filedOct. 16, 1997.

FIELD OF THE INVENTION

The present invention relates generally to the field of disc drive datastorage devices, and more particularly, but not by way of limitation, toan automated assembly of a disc drive head-disc assembly which includesa dynamic balance measurement station.

BACKGROUND

Modern hard disc drives are commonly used in a multitude of computerenvironments, ranging from super computers through notebook computers,to store large amounts of data in a form that can be made readilyavailable to a user. Typically, a disc drive comprises one or moremagnetic discs that are rotated by a spindle motor at a constant highspeed. The surface of each disc is a data recording surface divided intoa series of generally concentric recording tracks radially spaced acrossa band having an inner diameter and an outer diameter. Extending aroundthe discs, the data tracks store data within the radial extent of thetracks on the disc surfaces in the form of magnetic flux transitionsinduced by an array of transducers, otherwise commonly called read/writeheads. Typically, each data track is divided into a number of datasectors that store fixed sized data blocks.

The read/write head includes an interactive element such as a magnetictransducer which senses the magnetic transitions on a selected datatrack to read the data stored on the track. Alternatively, theread/write head transmits an electrical signal that induces magnetictransitions on the selected data track to write data to the track.

As is known in the art, each read/write head is mounted to a rotaryactuator arm and is selectively positionable by the actuator arm over aselected data track of the disc to either read data from or write datato the selected data track. The read/write head includes a sliderassembly having an air-bearing surface that causes the read/write headto fly above the disc surface. The air bearing is developed as a resultof load forces applied to the read/write head by a load arm interactingwith air currents that are produced by rotation of the disc.

Typically, a plurality of open-center discs and spacer rings arealternately stacked on the hub of a spindle motor. The hub, defining thecore of the stack, serves to align the discs and spacer rings around acommon centerline. Movement of the discs and spacer ring,s is typicallyconstrained by placing the stack under a compressive load andmaintaining the load by means of a clamp ring. Collectively the discs,spacer rings, clamp ring and spindle motor hub define a disc packenvelope or disc pack. The read/write heads mounted on a complementarystack of actuator arms, which compose an actuator assembly, commonlycalled an "E-block," accesses the surfaces of the stacked discs of thedisc pack. The E-block also generally includes read/write head wireswhich conduct electrical signals from the read/write heads to a flexcircuit which, in turn, conducts the electrical signals to a flexcircuit connector. The connector in turn is mounted to a flex circuitmounting bracket, and the mounting bracket is mounted to a disc drivebasedeck. External to the basedeck the flex circuit connector is securedto a printed circuit board assembly (PCB). For a general discussion ofE-block assembly techniques, see U.S. Pat. No. 5,404,636 entitled METHODOF ASSEMBLING A DISC DRIVE ACTUATOR issued Apr. 11, 1995 to Stefansky etal., assigned to the assignee of the present invention.

The head-disc assembly (HDA) of a disc drive is typically assembled in aclean room environment. The need for maintaining a clean roomenvironment (free of contaminants of 0.3 micron and larger) is to ensurethe head-disc interface remains unencumbered and damage free. Theslightest damage to the surface of a disc or read/write head can resultin a catastrophic failure of the disc drive. The primary causes ofcatastrophic failure, particularly read/write head crashes (anon-recoverable, catastrophic failure of the disc drive) are generallycharacterized as contamination, exposure to mechanically induced shock,and non-shock induced damage. The source of non-shock induced damage istypically traced to the assembly process, and generally stems fromhandling damage sustained by the disc drive during the assembly process.

Several factors that bear particularly on the problem of assemblyprocess induced damage are the physical size of the disc drive, thespacing of the components, the recording densities sought to be achievedand the level of precision to be maintained during the assembly process.The high levels of precision required by the assembly process arenecessary to attain the operational tolerances required by the discdrive. The rigorous operational tolerances are in response to marketdemands that have driven the need to decrease the physical size of discdrive while simultaneously increasing disc drive storage capacity andperformance characteristics. Demands on disc drive mechanical componentsand assembly procedures have become increasingly more critical in orderto support capability and size in the face of these new market demands.Part-to-part variation in critical functional attributes in themagnitude of a micro-inch can result in disc drive failures.Additionally, as disc drive designs continue to decrease in size,smaller read/write heads, thinner substrates, longer and thinneractuator arms, and thinner gimbal assemblies will continue to beincorporated into the drives, significantly increasing the need toimprove the assembly processes to protect the read/write heads and discsfrom damage resulting from incidental contact between mating components.The aforementioned factors resultingly increase the difficulty ofassembling disc drives. As the assembly process becomes more difficult,the need to invent new tools, methods, and control systems to deal withthe emerging complexities pose unique problems in need of solutions.

Coupled with the size and performance improvement demands are furthermarket requirements for ever-increasing fault free performance. Inresponse to demands for enhanced reliability, some solutions have begunto emerge. Some disc drives have incorporated the use of ramp loadtechnology. By incorporating ramp load technology the need to physicallymerge the E-block assembly with the disc pack during the assemblyprocess is circumvented. The read/write heads are not loaded onto themedia until after completion of assembly and the drives are spun-up forthe first time. The improved performance is obtained by eliminatingread/write head induced media damage, basically by insuring an airbearing is present prior to the read/write heads being loaded to thediscs.

Ramp load technology is generally limited to smaller disc drive systems,namely sub 3.5 inch form factors, because those disc drives haverelatively few discs so tolerance stack-ups do not become a major factorin the assembly process. Increases in disc diameter, coupled withincreasing the number of discs in the disc pack, heighten the demands ofmaintaining the dimensional, mechanical and operational integritybetween the E-block and the disc pack. Tolerance stack-ups become verycritical in the assembly process and conformation of dimensionalattributes of the disc pack and the E-block assembly must be made priorto any attempts in merging the two. Dependence on ramp load technologyas the means to accomplish the head-disc merge for larger diameter,multiple surface disc packs would permit a number of E-block to discpack interface mismatches to escape the process, resulting insub-optimal performance or even failure of the product. Ramp loadtechnology fails to provide the precision and repeatability required bylarger and more complex disc drives.

The progression of continually decreasing disc thickness and discspacing, together with increasing track density and increasing numbersof discs in the disc pack, has resulted in a demand for tools, methodsand control systems of ever increasing sophistication. A result of thegrowth in demand for sophisticated assembling equipment has been that adecreasing number of assembly tasks involve direct operatorintervention. Many of the tasks involved in modern methods are beyondthe capability of operators to reliably and repeatably perform.

In addition to the difficulties faced in assembling modern, highcapacity, complex disc drives, actual product performance requirementshave dictated the need to develop new process technologies to ensurecompliance with operating specifications. The primary factor drivingmore stringent demands on the mechanical components and the assemblyprocess is the continually increasing areal densities and data transferrates of the disc drives.

The continuing trend in the disc drive industry is to develop productswith ever increasing areal densities, decreasing access times andincreasing rotational disc pack speeds. These three factors, incombination, place greater demands on the ability of modern servosystems to control the position of read/write heads relative to datatracks. As track densities continue to increase, a significant problemthat results is the ability to assemble HDAs nominally free from theeffects caused by unequal load forces on the read/write heads, disc packimbalance or one of the components of runout, velocity and acceleration(commonly referred to as RVA). The components of RVA are: disc runout (ameasure of the motion of the disc along the longitudinal axis of themotor as it rotates); velocity (a measure of variations in linear speedof the disc pack across the surface of the disc) and acceleration (ameasure of the relative flatness of the discs in the disc pack). Bydesign, a disc drive typically has a discreet threshold level ofresistance to withstand rotationally induced noise and instability,below which the servo system is not impaired. Also, a fixed range ofload forces must be maintained on the read/write head to ensure properfly height for data exchange. The primary manifestations of mechanicallyinduced noise and instability are (1) vibration induced read/write headoscillation, (2) beat frequencies written into the servo signal at theservo write station and (3) non-repeatable runout. Oscillations areoften introduced to the system via (1) deformations of the disc surface,(2) harmonics induced by disc pack imbalance, or (3) excessive surfaceaccelerations encountered by the read/write head while flying on trackor traversing the disc surface during track seeks. Verification of discpack compliance to the RVA specifications is crucial to the overallquality and long term reliability of the product. To ensure RVAcompliance, measurements are taken to determine: (1) the amount ofrunout present in the disc pack, (2) absence of concave or convex discprofile as well as absence of a wavy disc profile across the surface ofthe discs, and (3) absence of a wavy disc profile around each trackcircumference.

The foregoing measurements require sophisticated metrologicalinstruments and techniques. The complexity of the measurements renderthem very difficult for an operator to perform, particularly at highassembly run rates. Specific problems arising out of operator executedor operator assisted measurements include the frequency of damage to thediscs and inconsistent and/or inaccurate measurement results obtainedfrom a manually based measurement process. Both component damage andmeasurement errors occur from operator inability to maintain asufficiently close interface with the measurement instruments as isdemanded by the measurement process and associated instruments.

Damage to disc surfaces can cause read/write head crashes, while discpacks not in compliance to the surface acceleration profiles are knownto cause at least three distinct problems in disc drive performance. Thefirst problem relates to disc drive response to a concave or convex discsurface. A concave surface causes the fly height of the read/write headto decrease. A decrease in fly height increases the signal to noiseratio during read-write functions, but increases the read/write headsusceptibility to surface aspirates that disrupt the air bearing,causing the read/write head to lose flight stability. A convex surfacecauses the fly height of the read/write head to increase. An increase infly height decreases the read/write head susceptibility to surfaceaspirates but also decreases the signal to noise ratio during read/writefunctions. A significant decrease in the signal to noise ratio can causedata errors and/or servo burst misreads which cause the disc drive tosuspend operations.

The second problem arising from non-complying disc packs relates to thedrive response to radially wavy profiles across the surface of the discsin the disc pack. A disc profile of this nature causes abrupt changes inthe read/write head fly height during seek operations. Abrupt changes infly height encountered during seek operations can send the read/writehead into oscillation, causing the read/write head to miss or misread atrack-crossing, resulting in an overshoot or undershoot of the seektrack. Furthermore, an abrupt change in fly height during a seekoperation can cause contact that damages the disc and/or the read/writehead. In a worst case, the contact can be of an intensity that resultsin a read/write head crash.

The third problem caused from non-complying disc packs is similar innature to the second problem as it also relates to the disc driveresponse to wavy profiles. However, the wavy profiles of concern forthis problem are circumferentially wavy disc surface profiles. Theproblem that is encountered when a read/write head encounters acircumferentially wavy disc surface profile is read/write headoscillation following a seek operation or during a track followingoperation. As with the radially non-flat surface, the circumferentiallynon-flat surface causes abrupt chances in read/write head fly heightinducing the same type of responses described above, i.e., flightinstability, oscillation, disc contact, read/write head crashes and evenloss of servo lock.

Typically, in a phase lock loop servo system, after each seek a settlingtime is required to allow for seek induced read/write head oscillationto dampen out and allow the read/write head to come on track. Read/writehead instability often results in the disc drive having, an inability toread the information contained in its servo frame. If instabilityremains at the end of the allocated settle time, the disc drive willnormally retry the function. After a set number of unsuccessful retriesthe disc drive reports a failure to the system and discontinues the seekprocess. However, should the system attain servo lock, a mechanicallyinduced noise causing read/write head oscillation of sufficient durationwill cause the system to lose its lock and malfunction.

The operating performance of the disc drive servo system is affected bymechanical factors beyond the effects of mechanically induced read/writehead oscillation from disc surface anomalies. Beat frequencies writteninto the servo frames during the servo track writing, process can causeservo system failure to phase lock, to lock to an inappropriate signal,or to lose phase lock and fall off track. Beat frequencies are typicallycaused by bernelled bearings (flat spots on a bearing surface resultingfrom handling or assembly damage), or by disc pack imbalance. Mechanicalnoise can cause perceived amplitude changes in the servo burst signalsthrough acceleration induced fly height changes. Shifts in servo burstsignal amplitudes, perceived or real, cause the servo system to adjustthe position of the read/write head. If the signals are false, the servosystem can drive the read/write heads off track, causing the drive tohalt operations. Additionally, mechanical noise can supply frequencyresponse mis-queues to the servo system. The frequency responsemis-queues are a result of harmonics being generated by the mechanics inthe same frequency range as the servo system crossover frequency. Eitherphenomenon can cause the servo system to drive the read/write head offtrack.

Another form of mechanical noise induced malfunction of the servo systemis runout. One intent of a disc drive design is to have nominallyconcentric data tracks. Concentricity of a data track is measured fromthe ideal or theoretical center of rotation of the disc pack. From theperspective of the read/write head, each data track is positioned afixed distance from the theoretical center of rotation the disc pack.Servo systems are designed with this geometric relationship in mind. Ifthe actual concentricity of the data track excessively or abruptlydeviates from the theoretical concentricity the servo system will beincapable of responding with appropriate corrections to allow the servosystem to maintain its phase lock, a condition required to assure thatread/write heads stay on track.

A related problem that occurs as track densities increase is variationin the width of the tracks. Whereas such variations in track width havenot been a significant factor in obtaining accurate servo control inprevious disc drives having relatively lower track densities, as trackdensities continue to increase variations in track width becomeincreasingly significant. Such variations in track width can occur as aresult of imperfections in the magnetic media of the discs, or can occuras a result of errors in the servo track writing process duringmanufacturing. Errors are traceable to the same family of disc packimbalance and RVA noise sources discussed hereinabove. Even withimproved approaches to the generation of position error signals in thedisc drive servo system, the ability of the system to deal with suchissues is finite. The limits of the servo system capability to reliablycontrol the position of the read/write head relative to the data trackmust not be consumed by the noise present in the HDA resulting from theassembly process. Consumption of the available margin by the assemblyprocess leaves no margrin in the system to accommodate chances in thedisc drive attributes over the life of the product. An inability toaccommodate changes in the disc drive attributes leads to field failuresand an overall loss in product reliability, a detrimental impact toproduct market position.

Although the servo system is the system primarily affected bymechanically induced system noise, the disc drive read-write channel isequally dependent upon the mechanical integrity of the HDA. The issuesdiscussed hereinabove regarding the inability of an oscillatingread/write head to accurately read servo data also applies to read-writedata. However, it is typical for read-write data to demonstrate a muchlower signal to noise ratio than is present in the disc drive servoburst signals and gray code, thereby rendering read/write headcapability in read data fields more susceptible to read errors. Readerrors have frequently been traced to head-disc misalignments of thetype causing a change in the fly height characteristics of theread/write head. Changes in fly height that increase the fly heightcause the read/write head transducer to be located farther away from thedata fields. The increased distance between the transducer and the datafield imparts the perception of a decrease in data bit field strengthrelative to the background noise, resulting in an inability to read thedata contained in the data field. Attempts to perform accuratemeasurements of head-disc misalignments occurring as a result of discpack tilt have not been successful in manual head-disc merge operations.The inability to verify the presence of a head-disc misalignment duringthe read/write head-disc merge operation leads to rework of disc drivesthat subsequently fail in the disc drive production process. Reworkingof disc drives exposes the disc drive, in particular the disc drive HDA,to increased handling, thereby increasing, the probability of damage tothe disc drive.

Components of modern disc drives have a relatively high susceptibilityto damage induced through mechanical shock. One type of shock induceddamage presented by prior merge operations deals with the problem of"head slap." Head slap is a term used to describe the dynamics of aread/write head, resting on a disc, in response to mechanically inducedshock. The shock causes the read/write head to lift off the disc, andonce off the disc the gimbal spring cants the read/write head as theforce of the load arm drives the read/write head back to the disc.Typically, the first point of contact of the read/write head are thecorners thereof against the disc surface. It is known that shocks of aload of greater than 20 grams for duration of 0.5 milliseconds or lesswill cause head slaps. It is also well known that the results of headslaps often lead to read/write head crashes.

Taken in combination--the tasks involved in assembling a modern discdrive exceeds the capability of manual assemblers; the susceptibility ofthe disc drive to damage during the assembly process; the level ofprecision assembly required by increasing areal densities; and the needto minimize adverse effects of mechanically induced noise on the discdrive servo system--have culminated to render prior disc drive assemblymethod archaic.

Thus, in general, there is a need for an improved approach to disc driveassembling technology to minimize the potential of damage duringassembly, to produce product that is design compliant and reliable, andto minimize mechanically induced system noise. More particularly, thereis a need for an automated dynamic balance correction of a disc drive.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for determining the dynamicbalance of a disc stack, the disc stack having a spindle drive motorwith a plurality of discs attached thereto. The apparatus provide for anautomated assembly procedure that requires minimum operator attentionwhile performing a dynamic imbalance test on the disc stack.

A balance measure assembly station is disclosed having a conveyor whichtransports a pallet supporting disc drive component, the componentsincluding a disc drive motor having one or more discs forming a discstack. The pallet has a bar code label identifying the pallet, and thebar code enabling the assignment of particular components to each palletto track the status of the components through the assembly process.

The balance measure assembly station advances the disc drive to a firstselected position, whereat a rotary positioner assembly positions thedisc stack to align and power the disc drive motor. The rotarypositioner assembly has an extensible cylinder to lift and rotate thedisc stack, while a sensor senses an identifying aperture next to theelectrical contacts of the disc motor. The rotary positioner thenadvances the disc stack to a position so that the identifying aperture,and hence the electrical contacts of the disc drive motor, are properlyoriented. The rotary positioner subsequently lowers the disc stack ontothe pallet which is advanced to a second selected position.

In the second selected position a motor power assembly has an extensiblebottom clamp that lifts the disc stack from the pallet into clampingengagement with a cooperating top clamp. The bottom clamp has a set ofretractable power leads which extend to make electrical contact with theelectrical contacts of the disc drive motor.

The disc drive motor is electrically powered to spin the discs at aselected speed. The balance measure assembly station has a balance headassembly having a plurality of transducers to measure the magnitude andphase angle of the dynamic imbalance of the disc stack.

The magnitude and phase angle of the dynamic imbalance are recorded to aproduction control computer system, and made available to other stationcontrol systems for use thereby, for example, to a balance correctionassembly station that applies weighted shims as required to the discdrive motor to balance the disc stack.

These and various other features as well as advantages whichcharacterize the present invention will be apparent from a reading ofthe following detailed description and a review of the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a disc drive of the type that is assembled bythe method and apparatus of the present invention. The housing cover ispartially cutaway.

FIG. 2 is a diagrammatic, top plan view of an automated disc driveassembly line constructed in accordance with the present invention forthe automated assembly of the disc drive of FIG. 1.

FIG. 3A is an end view of a pallet of the type used by the disc driveassembly line of FIG. 2.

FIG. 3B is a top view of the pallet of FIG. 3A.

FIG. 3C is an opposite end view of the pallet of FIG. 3A.

FIG. 4 is an isometric view of an automated balance measurement stationwhich forms a part of the disc drive assembly line of FIG. 2.

FIG. 5 is an isometric view of a portion of the automated balancemeasurement station of FIG. 4.

FIG. 6 is a bottom end view of the spindle motor of the disc drive ofFIG. 1.

FIG. 7 is an elevational view of the spindle motor of FIG. 6 having aplurality of discs and spacers mounted thereon, and clamped together bya clamping ring to form a disc pack.

FIG. 8 is a top view of the spindle motor of FIG. 7 without the discs,spacers, and clamping ring.

FIG. 9 is a partial sectional view alone the line 9--9 in FIG. 8.

FIG. 10 is an isometric view of the balance correction station whichforms a part of the disc drive assembly line of FIG. 2.

FIG. 11 is a partial exploded isometric view of the balance correctionstation of FIG. 10.

FIG. 12 is a top view of a shim used by the balance correction stationto dynamically balance the disc pack.

FIG. 13 is a partial sectional view of a compliant collet assembly ofthe balance correction station of FIGS. 10 and 11.

FIG. 14 is a partial sectional view of another compliant collet assemblyof the balance correction assembly of FIGS. 10 and 11.

FIG. 15 is an isometric view of the shim attachment assembly of thebalance correction station of FIGS. 10 and 11.

FIG. 16 is an isometric view of a portion of the shim attachmentassembly of FIG. 15.

FIG. 17 is an isometric view of the shim attachment assembly of FIG. 16,with the pin guide and shroud removed to show the shim spreaderassembly.

FIG. 18 is a partial sectional view of a spreader pin of the spreaderassembly of FIG. 17.

FIG. 19 is a top view of the shim attachment assembly of FIG. 15.

FIG. 20 is a partially cutaway, elevational view of the shim attachmentassembly of FIG. 19.

FIG. 21 is an isometric view of a head-disc merge station of the discdrive assembly line of FIG. 2.

FIG. 22 is an isometric view of a portion of the head-disc merge stationof FIG. 21.

FIG. 23 is an isometric view of the pack nest assembly of the head-discmerge station of FIG. 21.

FIG. 24 is a partially cutaway, top plan view of the pack nest assemblyof FIG. 23.

FIG. 25 is a partial sectional view of the pack nest assembly of FIG.24.

FIG. 26 is an isometric view of the end effector assembly of thehead-disc merge station of FIG. 21.

FIG. 27 is an elevational view of the end effector assembly of FIG. 26.

FIG. 28 is a partially cutaway, top view of a merge slide assembly ofthe head-disc merge station of FIG. 21.

FIG. 29 is a partial sectional view of the merge slide assembly takenalong the line 29--29 of FIG. 28.

FIG. 30 is an isometric view of the E-block nest assembly of thehead-disc merge station of FIG. 21.

FIG. 31 is a partial sectional view of the collet assembly of theE-block nest assembly of FIG. 30.

FIG. 32 is a top view of the magnet load assembly of the head-disc mergestation of FIG. 21.

DETAILED DESCRIPTION

Referring to the drawings in general, and more particularly to FIG. 1,shown therein is a top view of a disc drive 100 constructed inaccordance with the present invention. The disc drive 100 includes abasedeck 102 to which various disc drive components are mounted, and atop cover 104, which together with the basedeck 102 provides a sealedinternal environment for the disc drive 100. The top cover 104 is shownin a partial cut-away fashion to expose selected components of interest.It will be understood that numerous details of construction of the discdrive 100 are not included in the following description as such are wellknown to those skilled in the art and are believed to be unnecessary forthe purpose of describing the present invention.

Mounted to the basedeck 102 is a spindle motor 106 to which a pluralityof discs 108 are mounted and secured by a clamp ring 110 for rotation ata constant high speed. Adjacent the discs 108 is an actuator assembly112 (sometimes also referred to as an "E-block") which pivots about acartridge bearing 114 in a rotary fashion. The actuator assembly 112includes actuator arms 116 (only one shown) that support load arms 118.Each load arm 118 in turn supports read/write heads 120, with each ofthe read/write heads 120 corresponding to a surface of one of the discs108. As mentioned hereinabove, each of the discs 108 has a datarecording surface divided into concentric circular data tracks, and theread/write heads 120 are positionably located over data tracks to readdata from, or write data to, the tracks.

The actuator assembly 112 is controllably positioned by way of a voicecoil motor assembly (VCM) 122, comprising an actuator coil 124 immersedin the magnetic field generated by a magnet assembly 126. A latchassembly 127 is disposed to latch the actuator assembly in apredetermined park position when the disc drive 100 is turned off. Amagnetically permeable flux path such as a steel plate 130 (sometimesreferred to as a pole piece 130) is mounted above the actuator coil 124to complete the magnetic circuit of the VCM 122. When controlled DCcurrent is passed through the actuator coil 124, an electromagneticfield is set up which interacts with the magnetic circuit of the VCM 122to cause the actuator coil 124 to move relative to the magnet assembly126 in accordance with the well-known Lorentz relationship. As theactuator coil 124 moves, the actuator assembly 112 pivots about thecartridge bearing assembly 114, causing the heads 120 to move across thesurfaces of the discs 108 thereby allowing the heads 120 to interactwith the data tracks of the discs 108.

To provide the requisite electrical conduction paths between the heads120 and disc drive read/write circuitry (not shown), read/write headwires (not separately shown) are routed on the actuator assembly 112from the heads 120, along the load arm 118 and the actuator arms 116, toa flex circuit 134. The read/write head wires are secured by way of asuitable soldering process to corresponding pads of a printed circuitboard (PCB) of the flex circuit 134. The flex circuit 134 is connectedto a flex circuit bracket 136 in a conventional manner, which in turn isconnected through the basedeck 102 to a disc drive PCB (not shown)mounted to the underside of the basedeck 102. The disc drive PCBprovides the disc drive read/write circuitry which controls theoperation of the heads 120, as well as other interface and controlcircuitry for the disc drive 100.

FIG. 2 is a diagrammatic representation of a disc drive assembly line138 constructed in accordance with the present invention. The majorcomponents of the disc drive assembly line 138 are as follows: a palletload station 140; a disc install station 142; a clamp ring installstation 144; a runout-velocity-acceleration (hereinafter "RVA") station146; a balance measurement station 148; a balance correction station150; a balance verification station 152, a head-disc merge station 154;a filter install station 156; a cover install station 158; and a lineoff-load station 160.

Each of the stations has a station control computer (as noted) tocontrol the movements and sequences of the functions performed therein.In addition, all of the station control computers are linked to aproduction system computer (not shown) which passes information betweenstations and broadcasts information to all stations. It will beunderstood that the production system computer can be located at anydesired location, and being conventional, need not be described hereinwith regard to its construction or operation.

It will be noted from FIG. 2 that the general arrangement of thestations forms a characteristically rectangular layout. However, anyphysical arrangement between the pallet load station 140 and the lineoff-load station 160 can be used, such as a straight-line arrangement oran arcuate arrangement, as will be determined by such factors as theavailable floor space and other procedural requirements.

As will be discussed hereinbelow, the stations have conveyor portionswhich are joined to form a continuous conveyor 164 between the palletload station 140 and the balance measurement station 148, and likewisebetween the balance correction station 150 and the line off-load station160. A number of pallets 166 are shown at various positions along theconveyor 164. The pallet 166 shown at the line off-load station 160contains a completely assembled disc drive 100 when all the assemblyoperations of all the stations have been successfully completed. Thepallet 166 at the pallet load station 140 contains a plurality ofunassembled components which form the disc drive 100. Each pallet 166transports the components of the disc drive 100 to the stations, and incooperation with the stations, fixtures the components as appropriatefor the various assembly processes as will be described further below.

As discussed above, it will be noted from FIG. 2 that the generalrectangular arrangement of the conveyor 164 forms opposing legs, thefirst leg connecting the pallet load station 140 and the balancemeasurement station 148 and all the stations therebetween, and thesecond leg connecting the balance correction station 150 and the lineoff-load station 160 and all the stations therebetween. A transferconveyor 168 connects the balance measurement station 148 and thebalance correction station 150. Another transfer conveyor 168 provides aconveyor connection between the line off-load station 160 and the palletload station 140. In this manner it will be noted that FIG. 2illustrates a closed-loop conveyor 164 which permits a pallet 166 to bereturned to the beginning of the disc drive assembly line 138 ifnecessary, such as for repair or retest. A number of rotary transferconveyors 170 are used to shuttle and rotate the pallets 166 to and fromthe transfer conveyors 168.

Pallet Load Station

It will be noted from FIG. 2 that a first operator designated as 171attends the pallet load station 140 to provide a manufacturing record ofthe components used in each disc drive 100. A conventional bar codescanner and a computer keyboard (not shown) are provided forcommunication with both a station control computer (not shown) and theproduction system computer.

FIGS. 3A through 3B show the pallet 166 which has an identifying barcode label 172 that is scanned and reported to the production systemcomputer to track the pallet 166 through the disc drive assembly line138. Also recorded to the production system computer is the producttype, as well as a serialized identification of the base deck 102 andthe E-block 112, as well as lot number identification of the spindlemotor 106 and the magnet assembly 126.

The spindle motor 106 is supported by a bushing 165 in the pallet 166.The E-block 112 is supported by a pin 167 that supportingly engages thecartridge bearing 114. The magnet assembly 126 is located by a pair ofpins 169. The basedeck 102 is supported by a pair of supports 173 thatextend into an opening 175 in the pallet 166.

The latch 127 is preassembled as a subassembly of the basedeck 102 in anupstream assembly operation. Also pre-assembled to the spindle motor 106is a spider assembly consisting of an endcap supported by the top of thespindle motor 106, and having six streamers of a polyamide material,such as Kapton from Dupont, which are placed longitudinally along thespindle motor 106 to provide an even circumferential spacing between thespindle motor 106 and the discs 108.

Disc Install Station

As shown in FIG. 2, the disc install station 142 performs an automatedprocedure with minimum attendance by an operator. The disc installstation 142 is of conventional structure and need not be describedherein except as follows. Drawing details are not provided since such isnot considered necessary for a full understanding by a person skilled inthe art to produce the disc install station 142 or an equivalentthereof.

When the disc install station 142 is free, the station control computeradvances the conveyor 164 to release one of the pallets 166 into thedisc install station 142 work envelope. A conventional optical sensordetects the pallet 166 and pauses the conveyor 164 to operably positionthe pallet 166. A conventional bar code scanner reads the bar code label172 and queries the production system computer to determine the producttype to be built and queries a look-up table in a station controlcomputer (not shown) to determine the corresponding product disc packroutines.

A typical motor lift assembly raises to engage the bushing 165 in thepallet 166 to lock the pallet 166 in place, the motor lift assemblyhaving an extensible shaft that lifts the spindle motor 106 from thepallet 166. The disc install station 142 has a scanner which records tothe production system computer the lot identification of the discs 108used in the disc drive 100. A sensor verifies the presence of thespindle motor 106 to verify that the correct spindle motor 106 ispresent for the desired disc drive 100. If not, the spindle motor 106 isreturned to the pallet 166 and the pallet 166 is released by the stationcontrol computer without adding discs 108 to the spindle motor 106. Thestation control computer notifies the production system computer thatthe wrong spindle motor 106 was loaded, and the production systemcomputer reports the nonconformance to the pallet load station 140, andall downstream station control computers query the pallet load station140, as is described below, for an instruction to bypass thenonconforming disc drive 100 to prevent further value-added workthereto.

If the spindle motor 106 is correct, a conventional robotic arm picksand places the discs 108 and spacer rings onto the spindle motor 106 inappropriate sequence. When all the discs 108 and spacer rings have beenplaced on the spindle motor 106, the motor lift assembly lowers thespindle motor 106 back onto the pallet 166, and the pallet 166 isreleased so that the conveyor 164 can advance the pallet 166 to theclamp ring install station 144.

Clamp Ring Install Station

From the disc install station 142 the pallet 166 is conveyed to theclamp ring install station 144. The clamp ring install station 144 is ofconventional structure and need not be described herein except asfollows. Drawing details are not provided since such is not considerednecessary for a full understanding by a person skilled in the art toproduce the clamp ring, install station 144 or an equivalent thereof.

A scanner at the clamp ring install station 144 reads the bar code label172 and communicates with a station control computer (not shown) whichqueries the production system computer to determine whether the pallet166 is approved for further processing.

If approved, the pallet 166 is moved into an operable position in theclamp ring install station 144, whereat the conveyor 164 is paused. Aconventional motor lift assembly raises to engage the bushing 165 tolock the pallet 166, the motor lift assembly having an extensiblecylinder that lifts the spindle motor 106 out of the pallet 166. A clamppresenter supports the clamp ring 110 while it is inductively heated toincrease in diameter by thermal expansion. The clamp ring, afterexpansion, is presented to a clamping mandrel which provides a packingforce to the clamping ring to compress the stack of discs under theclamp ring 110. The clamp ring 110 conductively cools and shrinks intolocking engagement with the spindle motor 106.

The motor lift assembly lowers the spindle motor 106, discs I 08 and theclamp ring 110, which together will hereinafter be referred to as discpack 174 as shown in FIG. 7, onto the pallet 166. A second operator,designated 177, removes the spider assembly from the spindle motor 106and the pallet 166 is conveyed to the RVA measurement station 146.

RVA Measurement Station

From the clamp ring, install station 144 the pallet 166 is conveyed tothe runout-velocity-acceleration (hereinafter "RVA") measurement station146 where the runout, velocity and acceleration attributes of the discpack 174 are measured and recorded to another conventional stationcontrol computer (not shown). The RVA measurement station 146 is ofconventional structure and need not be described herein except asfollows. Drawing details are not provided since such is not considerednecessary for a full understanding by a person skilled in the art toproduce the RVA measurement station 146 or an equivalent thereof.

When the RVA measurement station 146 station control system is free, thestation control computer calls forth the pallet 166 from the clamp ringinstall station 144. A conventional bar code scanner reads the bar codelabel 172 and the station control computer queries the production systemcomputer to determine the eligibility for further processing. If thepallet 166 is rejected by any upstream station, the pallet 166 will passthrough the RVA measurement station 146 without further value-addedprocessing.

If accepted, the pallet 166 enters the RVA measurement station 146 to apoint where a conventional sensor detects the pallet 166 and signals theconveyor 164 to pause. A conventional rotary positioner raises to engagethe bushing 165 to lock the pallet 166 on the conveyor 164, the rotarypositioner having an extensible cylinder that lifts and rotationallyorients the disc pack 174 for proper alignment of the spindle motor 106with electrical supply contacts for functional testing thereof Therotary positioner then lowers the disc pack 174 to the pallet 166 andreleases the pallet 166, which is advanced to a second position adjacenta typical balance measurement assembly 178 where locking pins engage thepallet 166.

The balance measurement assembly 178 lifts the disc pack 174 intopressing engagement against an opposing supporting mandrel to clamp thedisc pack 174 for functional testing. The lifting portion of the balancemeasurement assembly 178 has integral power supply contacts whichelectrically contact the disc pack 174 to power the spindle motor 106.In this manner, the balance measurement assembly 178 powers the spindlemotor 106 to spin the discs 108 at a constant speed. The balancemeasurement assembly 178 activates conventional measurement transducersto measure and record the runout, velocity, and acceleration (RVA)characteristics.

The runout of the discs 108 is a measure of the axial variation of theheight of the disc 108 surface around a circumferential arc of aspecific radius. The velocity is a measure of the rate of chance of theaxial displacement of the disc 108 surface around a circumferential arcof a specific radius. The acceleration is a measure of the rate ofchange of the disc 108 velocity around a circumferential arc of aspecific radius.

The station control system compares the RVA readings to designspecifications, and accepts or rejects the disc pack 174 accordingly.The RVA test status is communicated by the station control computer tothe production system computer, and the pallet 166 is released from theRVA measurement station 146 for advancing to the balance measurementstation 148.

Balance Measurement Station

To this point in the disc drive assembly line 138 the disc pack 174 hasbeen conveyed through the pallet load station 140, the disc installstation 142, the clamp ring install station 144 and the RVA measurementstation 146. It will be understood that these stations are conventionaland that, if desired, the disc pack 174 can be assembled and tested forRVA attributes in semi-automatic, manually operated stations. For thepurpose of the present disclosure, the important aspect here is thestate of the disc pack 174 at this point of assembly as fed to the novelbalance measurement station 148 which will now be described.

Turning to FIG. 4, the balance measurement station 148 of the disc driveassembly line 138 has a framework 176 which supports a balancemeasurement assembly 178 and a conveyor assembly 180, the framework 176furthermore providing an enclosure 183 for a station control computer(not shown). A pair of upright supports 184 are supported on a topsurface 186 of the framework 176. The supports 184 support a baseplate188 which, in turn, supports both the conveyor assembly 180 and thebalance measurement assembly 178. A pair of opposing supports 190 areinterposed between the side rails 192 of the conveyor assembly 180 forsupport thereof The side rails 192 support a plurality of poweredrollers 194 which rollingly engage the pallet 166 (not shown).

FIG. 5 more clearly shows the balance measurement assembly 178 of thedisc drive assembly line 138, and it will be noted that the balancemeasurement assembly 178 has the following major components: a palletlocator assembly 196; a rotary positioner assembly 198; a motor powerassembly 200; and a balance head assembly 202.

The pallet 166 containing the disc pack 174 and other assemblycomponents is conveyed by the conveyor assembly 180 into the balancemeasurement station 148. A bar code scanner 204 (see FIG. 4) reads thebar code label 172 on the pallet 166 and communicates with the stationcontrol computer (not shown) which queries the production systemcomputer to determine the product type to be assembled and to verifythat the particular pallet 166 is approved for processing. If thepartially assembled disc drive 100 has failed any upstream testing, theproduction control computer (not shown) will not approve furtherprocessing and the pallet 166 will be passed through the balancemeasurement station 148 without further value-added processing.

If approved, the pallet 166 moves forward until a sensor (not shown)detects the pallet 166 and the station control computer (not shown)signals to pause the conveyor assembly 180. The rotary positionerassembly 198 rotationally orients the disc pack 174 for proper alignmentwith an electrical supply apparatus for powering the disc pack 174during functional testing. The rotary positioner assembly 198 has ashaft 212 that is extensible by a cylinder 214, the shaft 212 supportedfor rotation by a lower bearing 216 and an upper bearing 218. A distalend of the shaft 212 is attached to and rotates a housing 220. It willbe noted that the upper bearing 218 is supported by a movable supportplate 222, which, in turn, is guided by guide rods 224. The housing 220has an inner core which supports a fiber optic sensor 226. The shaft 212is rotated by a stepper motor 228 which operably engages the shaft 212by way of an interconnecting belt (not shown).

Turning now to FIGS. 6 and 7, it will be noted that the spindle motor106 has a motor housing 230 which supports an outer race 232, where themotor housing 230 and outer race 232 together spin freely around astationary shaft 234 by way of interior roller bearings (not shown)therebetween. The shaft 234 has a threaded shoulder 236 which enclosesthree electrical contacts 238 that are internally connected to thewindings (not shown) of the spindle motor 106. The electrical contacts238 are equally distributed in a common radial plane, as are threeindicating apertures 240 in an end face 242 of the shoulder 236, each ofthe indicating apertures 240 being adjacent to one of the electricalcontacts 238.

Returning now to FIG. 5, the support plate 222 is raised up against thestop nuts 243 by two air cylinders 245 which in turn raises the housing220, the shaft 212, and the sensor 226. The housing 220 engages thebushing in the pallet 166 to locate it. In this position, the sensor 226mounted in the shaft 212 is just below the surface of the spindle motor106. The shaft 212 is rotated by the stepper motor 228, which rotatesthe sensor 226 under the spindle motor 106. The sensor 226 rotatesthrough 120 degrees searching for the holes 240 in the spindle motor106. When one of the holes 240 is located, the shaft 212 is lifted byair cylinder 214 to lift the spindle motor 106 out of the pallet 166.The spindle motor 106 is rotated to orient the motor pins 238 with theelectrical contacts in the balance measurement assembly 178. The spindlemotor 106 is returned to the pallet 166 by disengaging the air cylinder214.

The pallet locator assembly 196 has a pair of locking pins 208 that areeach slidable mounted in a linear bearing 210 and attached to a distalend of an extensible cylinder 211 (only one shown) so that when thecylinders 211 are extended the locking pins 208 engage bushing apertures(not shown) in the bottom-side of the pallet 166. This second positionof the pallet 166 places the disc pack 174 adjacent the motor powerassembly 200 which supports and powers the disc pack 174.

The motor power assembly 200 has an extensible shaft 244 that isextended by a cylinder (not shown). A distal end of the shaft 244 has agripping ring 246 that pressingly engages the shaft 234 of the spindlemotor 106. The shaft 244 raises the disc pack 174 upward off the pallet166, and into opposing engagement with a tapered mandrel (not shown)which engages a central aperture 248 (FIGS. 8 and 9) in the top side ofthe shaft 234. The tapered mandrel is supported by a top block 250 andthe shaft 244 is supported by a bottom block 252, both blocks 250, 252being connected to a common web member 254 which is, in turn, mounted tothe balance transducer 262, which is mounted to a support 256. In thismanner the disc pack 174 is clamped on both ends of the motor shaft 234so that the discs 108 are free to rotate thereabout. It will be notedthat the tapered mandrel (not shown) is guided by guides 258 to preventit from rotating and is moved up and down by air cylinder 259 tovariably position the tapered mandrel relative to the gripping ring 246to compensate for different heights of the disc pack 174. After the discpack 174 is clamped, the shaft 244 and the tapered mandrel (not shown)are clamped by the air cylinders 261 to prevent movement of the shaft244 and tapered mandrel (not shown) during the test.

The shaft 244 has a set of retractable power supply leads 260 that arealigned with the electrical contacts 238 when the spindle motor 106 isin the reference position as provided by the rotary positioner assembly198 and discussed previously. In this manner, the motor power assembly200 provides electrical power to spin the disc pack 174. With the discpack 174 thus clamped and spinning, the balance head assembly 202 hasconventional transducers which determine the amount of dynamic imbalancepresent in the spinning disc pack 174. The balance head assembly 202consists of the fixture described above and a conventional two-planebalance measurement mechanism, with transducers 262 providing ameasurement of imbalance in two planes (top and bottom of the disc pack174). The two-plane balance measurement mechanism is of conventionalconstruction and well known to one skilled in the art, such as atwo-plane balancer made by American Hoffman model HDR11.1/SEK. Alsoincluded in the balance head assembly 202 is a timing mark sensor 264(see FIG. 4) that senses the timing mark 266 (see FIG. 8) to maintain aconstant rotational speed during measurements, and tracks the relativeposition of the timing mark 266 for phase angle calculation by thestation control computer (not shown). The phase angle of the netimbalance and the size of counter-weights that are required to bring thedisc pack 174 into compliance with the balance requirements of the discdrive design specification are calculated in a conventional manner bythe station control computer. The phase angles are referenced from thetiming mark 266. The station control computer (not shown) reports themagnitude and phase angle of disc pack 174 imbalance to the productioncontrol computer.

After the imbalance has been measured and transmitted to the productionsystem computer for future use by a downstream assembly station, thedisc pack 174 is de-energized and the shaft 244 retracts to return thedisc pack 174 to the pallet 166. The station control computer signalsrelease of the pallet 166. If space in the queue is available on thetransfer conveyor 168 (FIG. 2) the station control computer (not shown)activates conveyor assembly 180 to advance the pallet 166. The rotarytransfer conveyor 170 transfers the pallet 166 to the transfer conveyor168. Should the queue be full, the station control computer awaits asignal from the production system computer for clearance beforereleasing the pallet 166.

Balance Correction Station

Turning now to FIG. 10, shown therein is the balance correction station150 which receives information from the production system computerregarding the magnitude and phase angle of the imbalance of the discpack 174, as determined by the balance measurement station 148. It willbe noted that a framework 268 provides support for a balance correctionassembly 270 and a conveyor assembly 272, and further provides anenclosure 275 for a station control computer (not shown).

Upright supports 276 support a baseplate 278 that, in turn, supportsboth the conveyor assembly 272 and the balance correction assembly 270.A pair of opposing supports 280 are interposed between the side rails282 of the conveyor assembly 272 for support thereof. The side rails 282support a plurality of powered rollers 284 which rollingly engage thepallet 166, not shown in this figure, for advancement thereof.

FIG. 11, a generally exploded view of the balance correction assembly270, shows that the balance correction assembly 270 has the followingmajor components: a pallet locator assembly 286; a rotary positionerassembly 288; a shim selector assembly 290; a transfer assembly 292; aflipping assembly 294; and a shim attachment assembly 296.

The pallet 166 is conveyed by the conveyor assembly 272 into the balancecorrection assembly 270. A scanner (not shown) reads the bar code label172 on the pallet 166 to identify the product and to verify that thepartially assembled disc drive 100 is approved for further processing.If the partially assembled disc drive 100 has failed any upstreamtesting, for instance, the production system computer will not approvefurther processing and the pallet 166 will therefore pass through thebalance correction station 150 without further value-added processing.

An approved pallet 166 (not shown) is conveyed forward until a sensor(not shown) detects the pallet 166 and pauses the conveyor assembly 272.The pallet locator assembly 286 has a pair of locking pins 302 (only oneshown in FIG. 11) that are each mounted on a distal end of an extensiblecylinder 304 so that when the cylinders 304 are extended the lockingpins 302 engage bushings (not shown) in the bottom-side of the pallet166.

With a pallet 166 approved and secured by the locking pins 302, therotary positioner assembly 288 engages the disc pack 174 to raise thedisc pack 174 to a position adjacent a timing mark sensor 306 to locatethe timing mark 266 on the spindle motor 106 (FIG. 8). Based on theposition of the timing mark 266, the shim attachment assembly 296rotates the balance shim 314 (see FIG. 12) to a position relative to thetiming mark 266 for a proper installation. In the embodiment shown inFIG. 11, the rotary positioner assembly 288 has a shaft 308 that isextensible by a cylinder 310. A motor 309 in cooperation with a chain(not shown) rotates the shaft 308 to rotationally position the disc pack174. The timing mark sensor 306 is supported by an arm 312 which ismounted on an air driven slide (not shown). As the disc pack 174 israised by the cylinder 310, the arm 312 positions the timing mark sensor306 in radial alignment with the timing mark 266. The shaft 308 rotatesthe spindle motor 106 until the timing mark sensor 306 detects thetiming mark 266. The location of the timing mark 266 is thus recordedand used in subsequent operations that are discussed below. After thetiming mark 266 is found, the shaft 308 rotates to one of threepositions so as to clearingly pass through the bushing 165 of the pallet166. The cylinder 310 retracts to return the disc pack 174 to the pallet166, and the arm 312 moves to the right to clear the disc pack 174.

From the bar code label 172 the station control computer queries theproduction system computer to retrieve data from the balance measurementstation 148 which previously performed a dynamic balance measurementoperation to determine the magnitude and the phase angle of dynamicimbalance. To offset the dynamic imbalance, the balance correctionstation 150 can attach one or two shims 314 (shown in FIG. 12), asnecessary, to the spindle motor 106. A plurality of differently weightedshims 314 are stored and delivered for use by the shim selector assembly290.

Returning to FIG. 10, the shim selector assembly 290 has a rotatingcarousel 316 which holds a number of differently weighted shims 314 onappropriately dimensioned vertically standing rod supports. The carousel316 is rotated by a motor (not shown) to present the desired shim 314 toa pick and place robotic arm 318. The robotic arm 318 supportinglyengages the desired shim 314 in the carousel 316, and with a vacuumassisted end effector (which is not shown but which is of conventionalconstruction), picks the shim 314 from the carousel 316 and delivers theshim 314 to the shim attachment assembly 296.

The embodiment of the present invention as illustrated by FIG. 10 uses acarousel 316 which holds ten stacks of shims 314, so as many as tendifferently weighted shims 314 can be stored in the carousel 316. FromFIG. 12 it will be noted that the characteristic imbalance of aparticular shim 314 is determined by the width of a gap 319 in the shim314. For this embodiment of the invention it has been determined thatweighted shims 314 ranging in imbalance from 11.9 mg-in. to 69.5 mg-in.provide a sufficient range of shim weights to successfully balancesubstantially all expected imbalance conditions within a specifiedmaximum imbalance condition of 10 mg-in. per plane. For a furtherdiscussion of the selection and use of weighted shims for balancing adisc pack see U.S. Pat. No. 5,555,144 entitled BALANCING SYSTEM FOR ADISC DRIVE DISC ASSEMBLY issued Sep. 10, 1996 to Wood et al., assignedto the assignee of the present invention.

Continuing with FIG. 11, the transfer assembly 292 picks the disc pack174 from the pallet 166 and moves the disc pack 174 to the shimattachment assembly 296 for attachment of a selected shim 314 to thespindle motor 106. A top collet assembly 324 (FIG. 13) is utilized inconjunction with the transfer assembly 292 to maintain two importantrelational attributes of the disc pack 174. First, the rotationalposition of the timing mark 266 (on the spindle motor 106) must bemaintained so that the shim 314 is installed relative to the timing mark266. Also, a planar compliancy is necessary in engaging, the disc pack174 to accommodate for positional variation of the transfer assembly292.

The transfer assembly 292 has a two-axis positioner 320 which positionsa carrier 322, which in turn supports the top collet assembly 324 in ahorizontal direction along a horizontal guide 326 and in a verticaldirection along a vertical guide 328. The top collet assembly 324 isthus positioned above the disc pack 174 in the pallet 166 by thehorizontal and vertical movement of the two-axis positioner 320. It willbe noted that the top collet assembly 324 has a compliant mode, asdiscussed below, that provides for positive picking and positioning ofthe disc pack 174.

FIG. 13 is a partial sectional view of the top collet assembly 324 whichhas a fixed mode (depicted in FIG. 13) and an alternative compliantmode. The top collet assembly 324 is mounted to the carrier by aleveling plate 330. A collet 332 is attached at a first end 334 to acylinder 336, the top collet assembly 324 having a segmented end 338. Aflange portion 340 of the collet 332 extends radially and is constrainedby a pair of locking cylinders 342. In the fixed mode, the collet 332remains positionally fixed relative to the leveling plate 330. In thecompliant mode, the collet 332 has a two-axis freedom of movementrelative to the leveling plate 330, but the collet 332 does not rotate.The compliant mode provides for a self-centering of the top colletassembly 324 relative to the disc pack 174, while preventing rotation ofthe collet 332 so as to maintain the reference position of the timingmark 266.

In the fixed mode, each of the locking cylinders 342 retracts a shaft344 to engage a tapered lower pad 346 into a dimpled aperture 348 formedby the flange portion 340 of the collet 332. In the retracted mode, theshaft 344 has a shaft portion 350 that enters a passageway 352 in anupper pad 354 with a closely fitting relationship therebetween. Theposition of the locking cylinders 342 is thus fixed and determined bythe disposing alignment of the shaft portion 350 within the passageway352. The position of the collet 332 is thus fixed and determined by thewedging engagement of the lower pad 346 against the flange portion 340.

In the compliant mode, each of the locking cylinders 342 extends theshaft 344 to disengage the lower pad 346 from the flange portion 340. Inthe extended mode the shaft portion 350 is clearingly moved out of thepassageway 352 so that a reduced diameter portion 356 allows movement ofthe collet 332 relative to the leveling plate 330 which is positionablyfixed to the carrier 322.

In the compliant mode the collet 332 is free to move in the two-axisplane that is parallel to the plane of the surface of the disc pack 174that is engaged. The flange portion 340 slidingly engages the cylinder336 with a plurality of ball bearings 358 disposed therebetween. Asecond set of ball bearings 360 cooperate with a center race 362 tolimit the compliant motion to orthogonal movements in the x and y axisdirections, thus preventing rotary motion of the collet 332 in order tomaintain the reference position of the timing mark 266 on the disc pack174.

It will be noted from FIG. 13 that the top of the leveling plate 330 andthe bottom of the center race 362 (as depicted in FIG. 13) have parallelgrooves for receivingly engaging the ball bearings 360. It will furtherbe noted that the bottom of the flange portion 340 and the top of thecenter race 362 have parallel grooves, such grooves being orthogonal tothe grooves of the leveling plate 330 and the top of the center race362, for receivingly engaging ball bearings 360. This combination oforthogonal grooves in opposing surfaces allows orthogonal movement, butrotational forces will be resisted as shear forces on the ball bearings360.

When the top collet assembly 324 is in the compliant mode and positionedabove the disc pack 174 by the two-axis positioner 320, a tip 364 formedby the segmented end 338 is in position to engage the disc pack 174 inthe pallet 166. It should be noted that both the tip 364 and the centralaperture 248 have chamfered leading edges to urge the tip 364 into thecentral aperture 248.

Once the tip 364 is disposed within the central aperture 248, thecylinder 336 is energized to extend an actuator pin 366 which, in turn,moves a tooling ball 368. The tooling ball 368 moves downward andengages the segmented end 338 of the collet 332, causing the segmentedend 338 to diametrically expand. This results in the segments of thesegmented end 338 pressingly engaging and imparting a radial force onthe walls of the central aperture 248 sufficient to supportingly engagethe disc pack 174.

It will be noted from FIG. 11 that the two-axis positioner 320 lifts thedisc pack 174 upward and away from the pallet 166. After clearing thepallet 166, the locking cylinders 342 are energized to draw the lowerpad 346 against the flange portion 340 of the collet 332. This lockingof the locking cylinders 342 moves the collet 332, and hence the discpack 174, to a reference position of a known positive registrationrelative to the two-axis positioner 320.

The disc pack 174 is moved to the flipping assembly 294 above a bottomcollet assembly 380 (shown in FIG. 14) of the flipping assembly 294. Thebottom collet assembly 380 is similar to the top collet assembly 324,the exception discussed below. Because of this similarity the samenumber designations are used in FIG. 14 to designate identicalcomponents as such components are numerically designated in FIG. 13. Thedifference between the two collets is that the bottom collet assembly380 has an outside diameter gripping collet 384 rather than an innerdiameter gripping collet like the top collet assembly 324. FIG. 14 showsthat the bottom collet assembly 380 has a segmented end 382 of a collet384 that, when the cylinder 336 is retracted, causes a tip opening 388to grip the outside diameter of the shoulder 236 portion of the spindlemotor 106 (FIG. 7). As the two-axis positioner 320 lowers the disc pack174 into the flipping, assembly 294 both the top collet assembly 324 andthe bottom collet assembly 380 switch to the compliant mode. After theshoulder 236 portion of the spindle motor 106 has been gripped by thetip 388 of the bottom collet assembly 380, the top collet assembly 324withdraws and the bottom collet assembly 380 switches to the fixed mode.

The flipping assembly 294 has a rotary actuator 392 which positions thebottom collet assembly 380 in a fixed position above the shim attachmentassembly 296 in order to place the selected shim 314 on the clamp ring110 of the disc pack 174.

FIG. 15 is an isometric view of the shim attachment assembly 296 whichreceives the shim 314 from the shim selector assembly 290, androtationally positions the shim 314 relative to the timing mark 266 forproper dynamic balance. The shim attachment assembly 296 has a steppermotor 391 which supports a conventional pinion gear (not shown) thatengages a conventional rack gear (not shown) in order to linearlyadvance a shaft 393 which supports a platform assembly 396. In thismanner, the shim attachment assembly 296 moves the shim 314 verticallyuntil the shim 314 is correctly positioned adjacent the motor housing230, and attaches the shim 314 to the spindle motor 106. If necessary,one of the shims 314 is attached to each end of the spindle motor 106 todynamically balance the disc pack 174. FIGS. 16 and 17 show the majorcomponents of the shim attachment assembly 296 to be as follows: apositioning assembly 394, the rotating platform assembly 396; a guidancecontrol assembly 398; and a shim spreader assembly 400.

As shown in FIGS. 15 and 16, the positioning assembly 394 has aspringloaded centering mandrel 402 which is radiused at a leading endthereof to engage the central aperture 248 of the spindle motor 106 tocenter the spindle motor 106 relative to the shim 314. After theflipping assembly 294 has inverted the disc pack 174 so that the centralaperture 248 of the spindle motor 106 is adjacent the centering mandrel402, the bottom collet assembly 380 switches to the compliant mode. Inthis manner the disc pack 174 is centered with respect to a shim 314that is supported for attachment by the shim attachment assembly 296.

As will be clear below, the shim attachment assembly 296 can also attacha shim 314 to the bottom end of the spindle motor 106. In doing so, thepositioning assembly 394 provides for retraction of the centeringmandrel 402, by way of a spring-loaded cylinder (not shown), so that thecentering mandrel 402 is operably recessed below a centering ring 404which receivingly engages the shoulder 236 of the spindle motor 106 soas to likewise center the disc pack 174 with respect to a shim 314during attachment thereof to the bottom of the spindle motor 106.

Disposed generally about the positioning assembly 394 is the rotatingplatform assembly 396 which supportably rotates the shim 314 (see FIG.19) for attachment to the spindle motor 106. The rotating platformassembly 396 is positioned by the motor 309 (see FIG. 11) and chain (notshown) which is trained over both the shaft 308 and the rotatingplatform assembly 396. Rotation of the shim 314 is necessary in order toattach the shim 314 in alignment with the phase angle of dynamicimbalance as determined by the balance measurement station 148. Thepositioning assembly 394 has a pin guide 406 and a lower plate 408 whichare maintained in spaced-apart relation by a number of fasteners (notshown) which pass through apertures 410 in the pin guide 406. A shroud412 surrounds the pin guide 406 and the lower plate 408 to minimize thedisbursement of particulates that are generated by the shim spreaderassembly 400 during operation.

The guidance control assembly 398 has a plunger 414 which engages alinear voltage displacement transducer 416 (hereinafter sometimesreferred to as the "LVDT"). The LVDT 416 is positionable by a supportingbracket 418 (see FIG. 20) and provides position feedback of the distancefrom the top of the shim 314 to the bottom of the motor surface wherethe shim is going to be installed. The shim spreader assembly 400 opensthe shim 314 and moves up the distance calculated by the positionfeedback and closes the shim 314 on the spindle motor 106.

The shim spreader assembly 400 has a pair of spreader pins 420, each ofwhich having a portion thereof that extends above the pin guide 406 toengage an aperture 422 in the shim 314 (see FIG. 12). The spreader pins420 are constrained within guiding slots 424 formed in the pin guide406. The guiding slots 424 guide the spreader pins 420 in opposingdirections shown by directional arrows 426 in FIG. 12, so that as theshim 314 is spread open, the center of the shim 314 inner diameterremains substantially fixed and centered with respect to the positioningassembly 394.

FIG. 17 is a view of a portion of the rotating platform assembly 396with the pin guide 406 and the shroud 412 removed to better illustratethe support and operation of the shim spreader assembly 400. An aircylinder 428 moves the slider 430 up and down. The slider 430 isconstrained to vertical motion by a pair of opposing guides 432 (onlyone shown for clarity) and a guide rod 434 which is slidingly disposedwithin an aperture 436 in the slider 430.

FIG. 18 is a partial sectional view showing the manner in which theslider 430 is linked by a linkage 438 to each of the spreader pins 420,so that vertical movement of the slider 430 imparts articulatingmovement to the spreader pins 420. The linkage 438 has a ball 440 at afirst end that is receivingly disposed in a socket 442 of the slider430. The distal end of the linkage 438 is joined by a pin 444 to amedial portion of the spreader pin 420. At a lower end the spreader pin420 has a ball 446 that is disposed within a socket 448 in a base member450 that is attached to the lower plate 408. FIG. 18 represents therelationship of mating components of the shim spreader assembly 400 whenthe cylinder 428 is retracted, and thus the LVDT 416 has not beentriggered by the presence of a spindle motor 106. When a spindle motor106 does displace the LVDT 416 sufficiently so that the station controlcomputer energizes the cylinder 428, an upward motion of the slider 430imparts an outward motion of the spreader pins 420, in the direction ofarrow 426 as shown in FIG. 12.

It should be noted that the cylinder 428 has three modes. The first moderetains the spreader pins 420 in a home position awaiting the placementof shim 314. The second mode moves the spreader pins 420 to an openposition which spreads open the shim 314. The third position is a nullposition which allows the spreader pins 420 to float freely. The nullposition of cylinder 428 is used during the time the disc pack 174 isbeing removed from the shim spreader assembly 400 to minimize the amountof resistance from friction between the spreader pin 420 and the shim314.

In this manner the disc pack 174 is advanced to a fixed position abovethe shim attachment assembly 296 by the flipping assembly 294 for theattachment of the selected shim 314 to dynamically balance the disc pack174. Prior to the arrival of the disc pack 174, the robotic arm 318 hasalready picked the shim 314, as delivered thereto by the carousel 316,and delivered the shim 314 to the pin guide 406. In placing the shim 314onto the pin guide 406, the robotic arm 318 and the rotating platformassembly 396 cooperate to matingly align the spreader pins 420 with theapertures 422 of the shim 314.

Briefly summarizing, the shim attachment assembly 296 rotates to orientthe shim 314 relative to the timing mark 266 on the spindle motor 106 toprovide the appropriate dynamic balance, as prescribed by the balancemeasurement station 148. After the shim 314 is attached, the motor 391delivers the centering mandrel 402 of the positioning assembly 394 intopressing engagement with the top end of the spindle motor 106. Aspreviously described, the bottom collet assembly 380 is in the compliantmode so that the spindle motor 106 is able to seek the center of thepositioning assembly 394 by the cooperation of the centering mandrel 402and the central aperture 248.

The LVDT 416 controls the upward advancement of the shim attachmentassembly 296 to a reference position, whereupon the shim attachmentassembly 296 is advanced to a desired location where there is about0.050" clearance between the spindle motor 106 and the shim 314. Thusthe spindle motor 106 is very nearly touching the shim 314 before theshim 314 is spread open. In this manner the spindle motor 106 provides abacking surface for the shim 314 should any buckling of the shim 314occur during spreading.

After the shim attachment assembly 296 is in the desired backingposition, the cylinder 428 is energized to activate the shim spreaderassembly 400. The shim attachment assembly 296 finally positions theshim 314 so that the clamp ring 110 is substantially in coplanaralignment with the shim 314. At that time the cylinder 428 switches tothe null mode which allows the shim 314 to spring closed and clamparound the clamp ring 110. Finally, the shim attachment assembly 296 iswithdrawn from the disc pack 174 a short distance, while the rotatingplatform assembly 396 rotates the LVDT, and then moves up to a referenceposition to verify that the shim 314 is attached substantially squarelyon the spindle motor 106. When the measurement is satisfactorilycompleted, the shim attachment assembly 296 is withdrawn from the discpack 174.

With the shim 314 in place, the flipping assembly 294 returns the discpack 174 to the unrotated position. The transfer assembly 292 positionsthe top collet assembly 324, which is in the compliant mode, intosupporting engagement of the disc pack 174. The bottom collet assembly380 releases and the disc pack 174 is lifted out of the flippingassembly 294 and the bottom of the disc pack is moved, as necessary, toa fixed position above the shim attachment assembly 296.

With the shim attachment assembly 296 approaching the disc pack 174, thecentering mandrel 402 is retracted to provide the centering ring 404 formating alignment with the shaft 234 of the spindle motor 106. Asdescribed before, the centering ring 404 and shaft 234 cooperate toposition the spindle motor 106 in alignment with a second shim 314 thathas been selected and delivered to the pin guide 406. In the same manneras for the top of the motor, the shim 314 is rotated and attached to areceiving groove 452 of the spindle motor 106 (FIG. 7). The second shim314 is delivered to the shim spreader assembly 400 during the timeinterval that the disc pack 174 is being transferred from the flippingassembly 294 to the top collet assembly 324.

Once one or two of the balancing shims 314 have been attached to thebottom and top of the spindle motor 106, as needed, the transferassembly 292 returns the disc pack 174 to the pallet 166, and the pallet166 is released by the pallet locator assembly 286 to be conveyed to thebalance verification station 152.

Balance Verification Station

From the balance correction station 150 the pallet 166 containing thedisc pack 174 and other assembly components is conveyed to the balanceverification station 152, the next station in line in the disc driveassembly line 138. The balance verification station 152 is in everyrespect structurally and functionally identical to the balancemeasurement station 148 described hereinabove. For this reason it willnot be necessary to provide a detailed description of the balanceverification station 152.

The balance verification station 152 repeats the tests performed by thebalance measurement station 148 to determine whether the attachment ofthe weight shims 314, as specified by the balance measurement station148 and applied by the balance correction station 150, has reduced themagnitude of dynamic imbalance of the disc pack 174 to an acceptablelevel which falls below the specified limit. If so, the disc pack 174 isreleased from the balance verification station 152 and conveyed to themerge station 154 for further processing.

If the magnitude of imbalance is above the specified limit, however, thestation control computer of the balance verification station 152 reportsto the production system computer which, in turn, broadcasts a rejectionof the particular pallet 166 so that no further value-added work isperformed on the disc drive 100.

Head-Disc Merge Station

The pallet 166 holding the disc pack 174 is conveyed for processing atthe merge station 154 in the disc drive assembly line 138. FIG. 21 showsthe merge station 154 which automatically merges the disc pack 174, theE-block 112, and the magnet assembly 126.

It will be noted that a framework 453 supports a conveyor assembly 454and provides an enclosure 455 for a station control computer (notshown). Also supported by the framework 453 is a number of majorcomponents, as follows: a basedeck positioning assembly 456; a pack nestassembly 458; a transfer assembly 460; and a merge assembly 464. FIG. 22more clearly shows several of the components of the merge station 154.

The pallet 166 is conveyed into the merge station 154 by the conveyorassembly 454. A scanner (not shown) reads the bar code label 172 on thepallet 166 to identify the product being assembled and to verify thatthe particular partially assembled disc drive 100 is approved forfurther processing. If the disc pack 174 has failed any upstreamtesting, the production system computer will in effect reject the discdrive 100 and the pallet 166 will pass through the merge station 154without further value-added processing.

An approved pallet 166 (not shown) is conveyed forward until thebasedeck positioning assembly 456 pauses the conveyor assembly 454. Itwill be noted that the basedeck positioning assembly 456 has a sensor468 (not shown) which detects the pallet 166. The basedeck positioningassembly 456 furthermore has a locking pin 470 mounted to a basedecklift 472 which is attached to a distal end of an extensible cylinder 474so that when extended the locking pin 470 engages a bushing (not shown)in the bottom-side of the pallet 166. Once raised, the basedeckpositioning assembly 456 furthermore has a deck clamp assembly 476 (seeFIG. 21) attached to the conveyor assembly 454 which clamps the basedeck102 for positive support and positioning thereof.

As is discussed below, the pack nest assembly 458 orients the shaft 234of the spindle motor 106 to a desired location for mating alignment withcontact pads located on a printed circuit board assembly which isattached thereto in a downstream station.

From FIGS. 23 through 25 it will be noted that the pack nest assembly458 has a spindle 478 which is matingly engageable with the spindlemotor 106, as will be discussed fully below. The spindle 478 isvertically positionable by way of a motor 480 that is operably connectedto a gear 482 (see FIG. 24) which engages a rack 484. Rotation of themotor 480 thus imparts rotation to the gear 482 which, in turn, linearlyadvances the rack 484 which is attached to an external portion of ahousing 486 (see FIG. 25). The housing 486 is attached to a shaft 488that supports a nest block 490 which, in turn, supports the spindle 478.The motor 480 is a stepper motor with a feedback control provided by anumber of sensors 492 that detect the home position as well as forwardand reverse limits of travel in a conventional manner.

The shaft 488 is supported by a stationary housing 496 which encloses asleeve 498 that is journalled in a pair of bearings 500. In this mannerthe shaft 488 is slidingly disposed within the sleeve 498 for raisingand lowering the spindle 478. It will be further noted that the sleeve498 supports a pulley 502 that is operably connected to a motor 504having an encoder 505 for rotational positioning of the shaft 488.Rotation of the shaft 488 in this manner likewise rotates the nest block490 and the spindle 478.

The nest block 490 houses an extensible cylinder 506 which, whenextended, supports a stud 508 in an extended position adjacent thespindle 478. The nest block 490 further supports a sensor 510.

In operation, the pack nest assembly 458 raises the spindle 478 upwardto a position closely adjacent the bottom of the spindle motor 106,which is supported by the pallet 166. The motor 504 rotates the nestblock 490, and thus the sensor 510, sufficiently to locate one of thethree indicating apertures 240 on the spindle motor 106 (FIG. 6). Withthe indicating aperture 240 located at a relative position, the motor504 indexes the nest block 490 to align the stud 508 with the indicatingaperture 240 at the relative position. When the stud 508 is aligned withthe indicating aperture 240, the cylinder 506 is activated to extend adistal end of the stud 508 into the indicating aperture 240 at therelative position. The motor 504 rotates the stud 508 to a selectedreference position, that being the position which places the electricalcontacts 238 in alignment with pads on the printed circuit boardassembly which is installed in a downstream assembly station. With thespindle motor 106 so oriented for subsequent electrical connection, itwill be noted that the operations described in the following, areperformed by moving the disc pack 174 to various locations inthree-planar space, but that the spindle motor 106 is not rotated andthe electrical contacts 238 remain fixed at the reference position.

After aligning the electrical contacts 238 to the reference position,the motor 480 raises the spindle 478 to lift the disc pack 174 upwardfrom the pallet 166, thus presenting the disc pack 174 to the transferassembly 460.

Turning, now to FIG. 26, shown therein is an end effector 512 which issupported by the transfer assembly 460, the end effector 512 having abase 514 that supports a first top collet assembly 516 and a second topcollet assembly 518. The construction and operation of these colletassemblies 516, 518 is substantially the same as that of the top colletassembly 324 described above. As such, a detailed discussion of theconstruction of these collet assemblies 516, 518 would be duplicativeand therefore not necessary for an understanding of the transferassembly 460 of the present invention.

Further, FIG. 27 shows the end effector 512 has a pair of pins 520 and avacuum assisted suction cup 524 which engage the magnet assembly 126 forpicking from the pallet 166, as discussed in detail below.

FIG. 21 shows the base 514 is supported by a mount 526 which, in turn,is part of the transfer assembly 460 which also includes a three-axisservo table 525 which enables three dimensional positioning of the endeffector 512. The three-axis servo table is of conventionalconstruction, such as one manufactured by AccuFab Systems of Corvalis,Oregon, model 1250 controller and table.

In operation, the transfer assembly 460 positions the end effector 512above the pallet 166 and simultaneously positions the disc pack 174 andthe magnet assembly 126 for merging. The transfer assembly 460 positionsthe first top collet assembly 516 to supportingly engage the disc pack174. The transfer assembly 460 moves the disc pack 174 to a merge slideassembly 528, which receivingly supports and temporarily shuttles thedisc pack as described below. The transfer assembly 460 has locatingpins 520 and suction cup 524 that simultaneously supportingly engage themagnet assembly 126. The transfer assembly 460 thus moves the magnetassembly 126 to a magnet load assembly 532.

The transfer assembly 460 returns the end effector 512 to the pallet 166where the second top collet assembly 518 supportingly engages theE-block 112. A sleeve 527 receivingly engages a stop pin 531 (seeFIG. 1) of the E-block 112. The transfer assembly 460 moves the E-block112 to an E-block nest assembly 530.

FIG. 28 is a top view of the merge slide assembly 528, from which itwill be noted that a collet assembly 534 receivingly supports the discpack 174 (see FIG. 29). After the disc pack 174 is transferred by theend effector 512 to the collet assembly 534, a number of sensors 535supported below the disc pack 174 by the merge slide assembly 528 (seeFIG. 29) and supported above the disc pack 174 by the end effector 512(see FIG. 27), locate the position of the bottom and top discs 108. Thesensors 535 thus detect the overall height and squareness of the discpack 174.

These measurements are used by the station control computer to adjust ahead spreader assembly 537 (see FIG. 22) to optimize a spreading actionof the load arms 118 of the E-block 112 during merging. The headspreader assembly 537 has a comb 539 which is vertically positioned by acylinder 541 and linearly advanced into the E-block 112 by a cylinder543 to wedgingly provide sufficient clearance between opposing heads 120for the passage of the corresponding data disc 108 during mergeoperation. With the head spreader assembly 537 activated, a shippingcomb (not shown) is removed from the E-block 112 by a third operatordesignated as 539, and the disc pack 174 is moved back to the unshuttledposition, thereby merging the disc pack 174 and the E-block 112.

Returning to FIG. 28, the collet assembly 534 is supported by a slidingblock 536 that has a pair of slider bushings 538 (see FIG. 29) slidinglysupported on bearing shafts 540. The bearing shafts 540 are supported bya fixed block 542 which is attached to the base 514. The sliding block536 is linearly positioned by a cylinder 544 which is fixedly attachedat a first end to the fixed block 542 and which has an extensible rod546 that is attached to the sliding block 536. In this manner the colletassembly 534 is moveable between a merge position, as shown in FIG. 28,and a shuttled position where a surface 536 of the sliding block 534abuttingly engages a shock absorber 550 which extends from a surface 552of the fixed block 542.

FIG. 29, a sectional view taken along line 29--29 of FIG.28, shows thecollet assembly 534 having a cylinder 554 which drives an actuator pin556 against a tooling ball 558 which opens a collet 560. When thecylinder 554 is actuated, as shown in FIG. 29, the collet 560 clamps theinner bore of the threaded shoulder 236 of the spindle motor 106 insupporting engagement thereof Subsequent deactivation of the cylinder554 causes the actuator pin 556 to release the tooling ball 558 from thecollet 560 to release the clamping support of the disc pack 174.

Similar to collet assemblies previously described, the collet assembly534 is compliantly supported so as to provide two degree freedom ofmovement of the collet 560 for self-centering, about the shoulder 236while clamping thereto. This is accomplished by supporting the cylinder554 and all the components that depend therefrom on a cylinder adapter562 having extending portions receivingly disposed in a fixed nest block564 that is rigidly attached to the nest block 564. A slidingrelationship between the cylinder adapter 562 and the nest block 564 isprovided by a plurality of ball bearings 566 interposed therebetweenboth above and below the cylinder adapter 562 extending portions.

FIG. 30 is an isometric view of the E-block nest assembly 530 which hasa mount 568 supporting a bottom sleeve 570 which receives the stop pin531 (see FIG. 1) of the E-block 112. A sensor 572 measures the amount oftilt in the placement of the E-block on a collet assembly 574, stoppingthe merge process if the amount of tilt is beyond a specified amount Alatch pin 575 (see FIG. 27) has a tapered leading edge that slidinglyengages a surface 577 (see FIG. 1) of the latch 127, thereby rotatingthe latch 127 for passage of the stop pin 531 of the E-block 112 into alocking arm 579 (see FIG. 1) of the latch 127. With the stop pin 531thus positioned inside the locking arm 579, the cartridge bearing 114 ofthe E-block 112 is supported by the collet assembly 574 during the mergeprocedure.

FIG. 31 shows a partial sectional view of the E-block nest assembly 530wherein it will be noted that the collet assembly 574 is of similarconstruction as the top collet assembly 324 of FIG. 13, in that thecollet assembly 574 has an inner diameter gripping collet 576 that gripsthe cartridge bearing of the E-block 112 in the same manner that the topcollet assembly 324 grips the central aperture 248 of the spindle motor106. In the same manner as explained hereinabove, the collet assembly574 has a cylinder 578 that when activated engages a tooling ball 580against the collet 576 to spread a tip 582 into pressing engagement withthe E-block 112. The collet assembly 574 is also compliantly supportedwith respect to a mounting framework 584 by a plurality of ball bearings586 disposed between a collet supporting flange member 588 and a nestblock 590 that is rigidly supported by the framework 584. Furtherdetailed discussion of the construction of the collet assembly 574 isunnecessary in light of the previous discussion of collet assemblieshereinabove together with the similarities thereto.

Thus it will be understood that the E-block nest assembly 530 positionsand supports the E-block 112 for merging. The E-block 112 and the magnetassembly 126 are merged by the magnet load assembly 532, shown in FIG.32. The magnet load assembly 532 has a nest plate 592 with a locatingpin 594 which receivingly positions the magnet assembly 126 from the endeffector 512. The nest plate 592 is supported by a nest block 596 whichslidingly engages a slide 598. A first cylinder 600 is attached at afirst end to the base 514 by a supporting bracket 602 (FIG. 22) to whichthe cylinder 600 is pinned. An extensible rod of the first cylinder 600is attached to the nest block 596 by a supporting bracket 604 so thatextension of the first cylinder 600 imparts linear movement of the nestblock 596 and nest plate 592 along the slide 598.

The nest plate 592 is pivotally attached to the nest block 596 by abearing 606 and is supported for rotation about the bearing 606 by aslider bearing assembly 608. A second cylinder 610 has a first endpinned to the bracket 604 and an extensible rod attached to the nestplate 592 to impart rotation thereof about the bearing 606. In thesecond cylinder 610, in the extended position shown in FIG. 32, themagnet assembly 126 is in the final assembled position. In a retractedposition of the second cylinder 610, the magnet assembly 126 is rotatedto provide clearance with the E-block 112 during merging. In operation,therefore, both cylinders 600, 610 begin in a retracted position. Thefirst cylinder 600 first advances the magnet into a juxtaposed positionwith the E-block 112, and the second cylinder 610 rotates the magnetassembly 126 into final position.

With the merging of the disc pack 174, the E-block 112, and the magnetassembly 126 complete, the entire merged assembly is transferred by theend effector 512 to the basedeck 102. The end effector 512 supportinglyand simultaneously grasps each of the three assemblies. The disc pack174 is gripped by the first top collet assembly 516, and thereafter thecollet assembly 534 releases the disc pack 174. The E-block 112 isgripped by the second top collet assembly 518, and thereafter the colletassembly 574 releases the disc pack 174. The magnet assembly 126 issupported by the suction cup 524.

A spanner nut and a number of machine screws are placed in the bits ofelectric drivers 626 (FIG. 21) to secure the spindle motor 106, thecartridge bearing 114 of the E-block assembly 112 and the magnetassembly 126 to the basedeck 102. The transfer assembly 460 moves themerged components, while maintaining the merged interrelationship intothe basedeck 102. The electric drivers 626 secure the fastening hardwarethrough the basedeck 102 and into the component assemblies. The assemblycycle of merging the disc pack 174, E-block 112 and the magnet assembly126 thus completed, the pallet 166 is ready for release to the filterinstall station 156.

Filter Install Station

From the merge station 154 the pallet 166 containing the merged discpack 174, E-block 112 and the magnet assembly 126 is conveyed by theconveyor 164 to the filter install station 156 where a sensor locatesthe pallet 166 and a pair of extensible pins engage the bushing,s on thebottom of the pallet 166. A cylinder extends to supportingly lift thebasedeck 102 upward off the pallet 166 for work thereon. A fourthoperator, designated as 628, manually installs a recirculation filter(not shown) and a desiccant filter (not shown) in the basedeck 102. Thefourth operator 628 also secures the flex circuit bracket 136 to thebasedeck 102 and releases the pallet 166 to be conveyed to the coverinstall station 158 in the disc drive assembly line 138.

Cover Install Station

From the filter install station 156 the pallet 166 is conveyed by theconveyor 164 to the cover install station 158 where a sensor locates thepallet 166 and a pair of extensible pins engage the bushings on thebottom of the pallet 166. A cylinder extends to supportingly lift thebasedeck 102 upward off the pallet 166 for work thereon. A fifthoperator, designated as 630, places a gasket 632 (see FIG. 1) and thetop cover 104 onto the basedeck 102 and attaches fasteners through thetop cover 104 into the top of spindle motor 106, the cartridge bearing114 and the magnet assembly 126, and further, the fifth operator 630installs a number of fasteners to attach the top cover 104 to thebasedeck 102.

Line Off-Load Station

From the cover install station 158 the pallet 166 is conveyed by theconveyor 164 to the off-load station 160 where a sixth operator,designated as 634, determines from the production system computerwhether the assembled disc drive 100 is a completed and acceptable unit.The acceptable units are removed from the continuous conveyor 164 andplaced in a shipping queue. The unacceptable units are sent to thetransfer conveyor 168, for routing to the beginning station for repairor rework.

It is clear that the present invention is well adapted to attain theends and advantages mentioned as well as those inherent therein. While apresently preferred embodiment of the invention has been described forpurposes of the disclosure, it will be understood that numerous changescan be made which will readily suggest themselves to those skilled inthe art and which are encompassed within the spirit of the inventiondisclosed and as defined in the appended claims.

What is claimed is:
 1. An automated head and disc assembling apparatusfor assembling a disc drive from a plurality of component parts, thecomponent parts comprising a disc drive motor having a plurality ofdiscs attached thereto to form a disc stack, wherein the disc stack hasan electrical contact and an indicator mark adjacent thereto, theautomated head and disc assembling apparatus comprising:a balancemeasure station assembly to determine dynamic imbalance in the discstack, the dynamic imbalance being quantified as a resultant magnitudeand phase angle, the balance measure station assembly comprising: arotary positioner assembly for positioning the disc stack at a referenceposition, comprising:a first cylinder having an extensible rod with adistal end; a rotatable housing supported by the distal end of the firstrod to supportingly engage the disc stack; a stationary sensor adjacentthe housing; and a drive assembly for rotating the housing until thesensor detects the indicator mark, and thereafter rotating the rotatablehousing to position the housing so that the indicator mark is disposedat a predetermined position; a motor power assembly matingly alignedwith the disc stack at the reference position for powering the discstack; and a balance head assembly for determining the magnitude andphase angle of the disc stack dynamic imbalance.
 2. The automated headand disc assembling apparatus of claim 1 further comprising:a conveyorassembly spanning the balance measure station assembly for deliveringthe component parts into and out of the balance measure stationassembly; and a pallet supported by the conveyor, the pallet supportingthe disc stack at the rotary positioner assembly and at the motor powerassembly.
 3. The automated head and disc assembling apparatus of claim 2further comprising a conveyor control assembly which comprises:a sensordetecting the pallet at a predetermined position to signal the conveyorto pause; and a locking pin lockingly engaging the pallet while theconveyor is paused.
 4. The automated head and disc assembling apparatusof claim 1wherein the motor power assembly provides power to theelectrical contact of the disc stack, and wherein the motor powerassembly comprises:a second cylinder having an extensible rod; and anelectrical lead supported by the second rod and aligned with theelectrical contact when the indicator mark of the rotatable housing ispositioned at the predetermined position.
 5. The automated head and discassembling apparatus of claim 4,wherein the balance head assemblycomprises:a transducer for measuring the dynamic imbalance condition ofthe disc stack.
 6. The automated head and disc assembling apparatus ofclaim 5 further comprising a network database for storing identificationparameters of the component parts and for storing the measured dynamicimbalance of the disc stack.